The present invention relates to a method of forming conductive structures on a semiconductor work object. More particularly, it relates to cleaning etched contact holes before metal plugs or other conductive structures are formed therein.
Every semiconductor chip has electrical connections between different devices or circuit component parts on the chip. The devices and components are associated with conductive structures to provide such connections. The formation of contact plugs, vias, metal lines and other conductive structures providing connectivity on a chip will generally be referred to herein as xe2x80x9cmetallizationxe2x80x9d.
In conventional processes, a contact or contact hole (or similar structure, such as a via) is etched in a layer of a dielectric material that is disposed over a layer of conductive material. Typically the dielectric material is a silicon oxide and the conductive material is a silicon substrate with dopant. The conductive material could also be another contact or via of silicon, tungsten, or polysilicon, for example. The contact is filled with a conductive material, typically a metal, to form a plug. The plug formed in the contact hole may consist of tungsten, aluminum, copper or other conductive material known in the art. An initial layer of a refractory metal such as Titanium is often first deposited on silicon at the bottom of the contact hole to form a silicide. Silicides help facilitate the electrical connection between the plug and silicon. A conductive barrier layer may also be placed between the conductive layer and the plug to control eutectic alloying, physical migration, or contamination. The barrier layer may also help anchor the plug into the contact hole. Titanium-tungsten (TiW) or titanium nitride (TiN) may be used to form a barrier layer. At the surface of the dielectric layer, the metal plug may be connected to thin lines of metal called leads, metal lines, as well as other interconnects, which connect the device associated with one conductive plug to another plug or other structure associated with a different device.
Metallization techniques are well known in the art. Certain such techniques are discussed in P. Van Zant, Microchip Fabrication: A Practical Guide To Semiconductor Processing (3rd ed. 1997) McGraw-Hill, New York, Chapters 5 and 13. Before a contact hole is filled with a conductive material to form a conductive plug, the hole is cleared of any contaminants including oxides, other resistive materials, and residuals (hereinafter such materials are referred to as xe2x80x9ccontaminant materialsxe2x80x9d) that may form or remain over the conductive region at the bottom of the contact hole. After wet etching to remove the contaminant material, further processing steps will form a plug of conductive material in the etched hole. If any appreciable amount of contaminants material remains at the bottom of the contact hole, it could impede current flow through the contact components or migrate into the underlying conductive layer. Therefore, contaminants are highly problematic for at least these reasons.
Cleaning and etching agents are used to remove contaminants before filling contact holes. Cleaning the contact hole is important, for example, to facilitate the formation of acceptable suicides at the bottom of the contact hole. Wet etchants are preferred for removing the contaminant material.
With the drive toward smaller chips with higher device densities, contact-hole widths are decreasing. Concurrently, contact holes are getting longer as they are required to extend through more layers on a die to reach the base silicon, polysilicon, or other conductive media. Consequently, the decreasing contact-hole widths and/or increasing contact-hole lengths means contact holes with high aspect ratios are becoming more prevalent. This is particularly true in the manufacture of DRAM memory chips.
The formation of conductive structures in small, high aspect ratio contact holes is especially problematic. Given the tight geometry of such holes, it is difficult, for example, to control conventional wet etchants so that they do not change the critical dimensions (CDs) of the contact hole during the process of removing oxides or other residual materials from the bottom of the contact hole.
Wet etchants especially affect CDs of small, high-aspect ratio contact holes. As etchant moves down the contact hole it becomes depleted as it reacts with the oxide sidewalls of the contact hole. Therefore, the etchant""s rate of reaction with oxide or other contaminant materials may be slower at the bottom of the contact hole and faster at the top of the hole. Unfortunately, because of the duration of time needed to the etch contaminant materials at the bottom of the contact hole, structural material at the top of the contact hole may be overetched during the process of removing the contaminants. This excessive etching may increase the width or diameter of the contact hole beyond specified critical dimensions.
When a contact hole exceeding critical dimensions is filled with conductive material to form a plug or other conductive structure, an oversized plug is formed. The oversized plug may be closer to adjacent or nearby conductive structures, creating a problem of electrical shorting.
To remove contaminants from small, high aspect ratio contacts, various conventional wet etchants may be used. Persons skilled in the art may choose from many available etchant technologies to remove the contaminants, including hydrofluoric (HF) in deionized (DI) water; HF/TMAH; HCL; and phosphoric and ammonia fluoride based solutions. Unfortunately, all of these solutions may adversely affect critical dimensions, as described above. Accordingly, priori art cleaning techniques are inherently problematic in their failure to preserve critical contact hole structures and dimensions.
The present invention overcomes the problems and disadvantages in the prior art by providing a process that preserves-contact hole CDs while allowing removal of contaminant contacts from the bottom of the contact hole (or other region adjacent a conductive region). Accordingly, the present invention improves production yields of dies having contact with small, high aspect ratios. Further, the present invention helps make higher density chips possible.
In one novel embodiment, the present invention provides a method of preparing a contact hole to receive a conductive plug comprising: providing a work object having a conductive layer adjacent a dielectric layer, and a contact hole disposed in the dielectric layer, the contact hole having surfaces that include sidewalls formed in the dielectric layer and a bottom defined by the conductive layer, the contact hole having an opening for receiving a conductive plug material; and depositing a layer of protective material on at least the surface around the opening of the contact hole, the material deposited being sufficient to protect the CDs of the contact hole opening during an etch of the contact hole to remove any contaminant material disposed over the conductive layer at the bottom of the contact hole.
In another novel embodiment, the present invention provides a method of forming a conductive plug in a contact hole comprising: providing a work object having a conductive layer adjacent a dielectric layer, and a contact hole disposed in the dielectric layer, the contact hole having surfaces that include sidewalls formed in the dielectric layer and a bottom defined by the conductive layer, the contact hole having an opening for receiving a conductive plug material; depositing a layer of protective material on at least the surface around the opening of the contact hole, the material deposited being sufficient to protect the CDs of the contact hole opening during etching of the contact hole to remove any contaminant material disposed over the conductive layer at the bottom of the contact hole; etching the protective material at the bottom of the contact hole to expose the contaminant material while retaining protective material around the opening of the contact hole; and filling the contact hole with a conductive material to form a plug.
In another novel embodiment, the present invention provides a method of forming a conductive plug in a contact hole comprising: providing a wafer having a conductive layer comprising silicon adjacent a dielectric layer comprising silicon oxide, and a contact hole disposed in the dielectric layer, the contact hole having surfaces that include sidewalls formed in the dielectric layer and a bottom defined by the conductive layer, a contaminant material being disposed over at least a portion of the conductive layer defining the bottom of the contact hole, the dielectric layer having a surface in which the contact hole terminates in an opening opposing the bottom; depositing a layer of a barrier material on the work object, the layer having a substantially uniform thickness from the surface at the opening of the contact hole to the bottom of the contact hole; and depositing a layer of a protective material barrier around at least the opening of the contact hole; etching the material at the bottom of the contact hole to expose the contaminant material while retaining protective material around the opening of the contact hole; etching the contact hole to remove contaminant material disposed over the conductive layer at the bottom of the contact hole; and filling the contact hole with a conductive material to form a plug.
The foregoing novel embodiments may include other advantageous features, defining further novel embodiments. Some such features are noted below and may be added to one or more of the foregoing embodiments alone or in combinations. In this regard, the embodiments of the present invention may further comprise the step of depositing a layer of barrier material over the surfaces of the contact hole before deposition of the protective material, and etching the barrier layer at the bottom of the contact hole to expose any contaminant material, while retaining protective material around the opening of the contact hole following the etch of the barrier layer. The embodiments of the present invention may use a dry etch technique to etch the barrier layer at the bottom of the contact hole and a wet etch technique to etch any contaminant material exposed following the dry etch. The embodiments of the present invention may have a barrier layer material comprising a refractory metal based compound that extends from the surface at the opening of the contact hole to the bottom of the contact hole. The embodiments of the present invention may have a layer of protective material that comprises a refractory metal based compound extending from the opening of the contact hole to a selected depth into the contact hole. The embodiments of the present invention may have a conductive layer that comprises a silicon based material and a dielectric layer that comprises a silicon oxide based material.
The embodiments of the present invention may use a PVD process to deposit the layer of protective material. The embodiments of the present invention may use a CVD process to deposit the layer of barrier material. The embodiments of the present invention may use a protective material that is composed substantially of TiN.
In the embodiments of the present invention, the contact hole may have a high aspect ratio. Further, in the embodiments of the present invention the opening of the contact hole at the surface of the dielectric layer may have a width of about 2 microns or less. The aspect ratio of the contact hole may be about 3:1 or more.
The embodiments of the present invention may include the step of depositing a layer of a metal on the conductive layer at the bottom of the contact hole. The metal is deposited subsequent to the wet etch to remove contaminants from the bottom of the contact hole. In certain embodiments, the deposited metal is a refractory metal. The refractory metal may be Ti. In the embodiments of the present invention, it is further contemplated that a barrier layer may be deposited over the metal deposited at the bottom of the contact. The barrier layer may be TiN.
In the embodiments of the present invention, conductive plug may be composed substantially of Ag, Al, Au, Cu, or W. Where tungsten is the conductive plug material, a preferred barrier layer material is TiN.
In the embodiments of the present invention, it is contemplated that the contact hole may be a via or a container for a capacitor.
The foregoing novel embodiments and features of the present invention and other novel embodiments and features of the present invention are described below in more detail. It should be understood that the description contained herein is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the spirit of the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.